The present invention pertains generally to medical monitoring methods and devices for analyzing and displaying electrophysiologic signals, and more particularly to systems and methods for amplifying electrophysiologic signals detected at electrodes placed on a subject to provide amplified electrophysiologic signals to such a medical monitoring device.
Medical monitoring involves monitoring the body of a subject to determine the state of health of the subject and to detect, identify, and diagnose changes or abnormalities in the state of the body which may be indicative of problems, or for treatment evaluation. Medical monitoring may involve, for example, monitoring the motion of a subject""s body, temperature or chemical changes of the subject""s body, and/or audible or electrical signals reflected or generated by the subject""s body. For example, electroencephalography (EEG) is a form of medical monitoring wherein the electrical potentials of the subject""s brain are monitored by attaching electrodes to the subject""s scalp. In electromyography (EMG), electrical activity generated in the subject""s muscles is monitored using surface and/or needle recording electrodes. Medical monitoring may take place when a subject is at rest, in motion, or during the performance of a medical procedure. In some cases, medical monitoring involves monitoring the response of a subject to a stimulus. For example, evoked potential (EP) monitoring may be used to detect the electrical response of a subject""s nervous system to audible, visual, or electrical stimuli. Medical monitoring involving stimulus and response detection may be used in combination with EMG and various other medical monitoring methods as well.
Monitoring of the various physiologic signals generated by a subject""s body is typically performed using dedicated devices and/or systems. For example, EEG monitoring may be performed using a dedicated EEG monitoring system, by attaching electrodes to a subject to detect the electrical potential of the subject""s brain, amplifying and filtering the signals received from the electrodes for the desired frequency range of interest for EEG analysis, and providing the amplified and filtered signals to an EEG analysis system including software for further manipulating the EEG signals for analysis and a display on an EEG system monitor. Similarly, EMG monitoring may be performed using a dedicated EMG monitoring system, by placing electrodes on the subject to detect electrical activity generated in the subject""s muscles, amplifying and filtering the signals detected by the electrodes for the desired frequency range of interest for EMG signals, and providing the amplified and filtered signals to an EMG analysis system including software for further manipulating the EMG signals for analysis and display on an EMG system monitor. Other signals of interest, e.g., vital signs, may be monitored in a similar manner, with a separate dedicated system provided for each type or modality of monitored signal of interest. Each such dedicated monitoring system may include or be connected to a system for providing stimulus to a subject, and for analyzing the particular detected signal of interest in response to the stimulus provided.
U.S. patent application Ser. No. 09/295,167, entitled xe2x80x9cMedical Signal Monitoring and Display,xe2x80x9d by Wim van Drongelen, and assigned to the assignee of the present application, describes a medical signal monitoring system and method providing the capability for an operator of the system to display and analyze physiologic signals of various types, frequencies, and modalities. Such a system may be provided with data from various physiologic signal acquisition systems, including systems for acquiring electrophysiologic signals from electrodes positioned on a subject. The system may further be connected to auditory, visual, and/or electrical stimulator systems, for controlling the providing of stimulation to a subject, while analyzing the physiologic signals received in response to the stimulus provided. Such a system includes an operator-friendly user interface which allows an operator of the system to designate and control, display, and analyze the physiologic signals received by the system and stimulus provided thereby. Such an integrated system provides a full range of diagnostic capability in a single device for use in a doctor""s office, operating room, intensive care unit, or emergency department.
In a typical application of a medical signal monitoring system, a plurality of electrodes may be attached to the body of a subject. Electrophysiologic signals, picked up by the electrodes, are carried by leads to a signal amplifier which may be part of or separate from the medical monitoring system. The amplified signals may, for example, be filtered, digitized, and provided to the medical monitoring system for analysis and display. In this manner, several electrophysiologic signals, e.g., EEG and EMG signals, produced by a subject may be monitored continuously or periodically.
Electrophysiologic signals to be displayed and analyzed by a medical signal monitoring system are typically derived from the signals picked up by electrodes placed on a subject""s body in one of two ways, as either differential or referential electrophysiologic signals. Differential electrophysiologic signals are derived from the difference between the signals detected at two electrodes placed in a desired position on the subject. Differential electrophysiologic signals are typically derived by connecting the signals provided from each of two electrodes positioned on a subject to each of the two inputs of a differential amplifier. The output of the differential amplifier is an analog differential physiologic signal, which may be filtered for a desired frequency range of interest and converted, by an analog-to-digital converter, to a digital differential physiologic signal which is provided to a medical signal monitoring system for analysis and display. Referential electrophysiologic signals are derived from the signal detected at an electrode placed in a desired position on the subject with reference to a reference electrode placed on the subject. Multiple referential physiologic signals may be determined in this way by employing multiple electrodes positioned on the subject and by detecting the signals detected at each of these multiple electrodes with reference to a single reference electrode. Amplified referential physiologic signals may be filtered and digitized for analysis and display on a medical signal monitoring system. Selected differential physiologic signals may be obtained by combining multiple referential physiologic signals which are obtained using the same reference signal. This may be achieved by subtracting one digitized referential signal from another digitized referential signal to obtain the desired differential signal.
Typical medical signal monitoring systems are designed to employ electrodes positioned on the subject for either differential or referential signal detection, and include the appropriate amplifier and analysis circuitry and software for the type of signal (differential or referential) to be processed. For example, the Spirit signal monitoring system, made by Nicolet Instrument Corp., allowed a user to define up to four differential channels of, e.g., EEG signals. Cross-point switching devices were employed in the system to connect selected electrode input signals to the inputs of selected differential amplifier circuits to define differential signal channels of interest. Any combination of electrode inputs could be coupled by the switches to the amplifier channels. Some more advanced medical signal monitoring systems provide both differential and referential electrophysiologic signal detection. Such a system may allow an operator to select whether the input signals provided from electrodes to the system are to be interpreted as differential or a referential signal inputs. The medical signal monitoring system then amplifies and analyzes the signals received in such channels in an appropriate manner for the type of channel (differential or referential) selected.
What is desired is a medical signal monitoring system which receives and analyzes electrophysiologic signals from a plurality of electrodes positioned on a subject, which allows an operator of the system to select whether the signal received from each electrode is to be amplified in a differential or referential mode, and in which a signal received from any given electrode may be amplified in a combination of differential and referential signal channels. Thus, what is desired is a medical signal monitoring system which provides a user selectable combination of amplified differential and referential electrophysiologic signals from a set of electrode input signals.
The present invention provides a medical signal monitoring system and method which provides a selectable combination of referential and differential medical signals for analysis and display. A system and method in accordance with the present invention employs a combination referential and differential amplifier circuit. A combination referential and differential amplifier circuit in accordance with the present invention includes a plurality of electrode inputs, a plurality of medical signal amplifiers, and a switching device for selectively coupling each of the plurality of electrode inputs to the plurality of medical signal amplifiers in a manner so as to provide simultaneously a combination of referential and differential electrophysiologic signals for analysis and display on a medical signal monitoring system.
A combination referential and differential amplifier circuit in accordance with the present invention includes a plurality of electrode inputs. Each of the electrode inputs is adapted to be coupled to an electrode positioned on a subject for detecting electrophysiologic signals of the subject. At least one of the plurality of electrode inputs to the combination referential and differential amplifier circuit is a reference electrode input. The reference electrode input to the combination referential and differential amplifier circuit may be buffered in a conventional manner, to prevent unbalance between the referential signal, which will employ the electrophysiologic signal input to the reference electrode input of the combination referential and differential amplifier circuit, and other electrode input signals, which will be paired with the reference input signal. Thus, a single buffered reference electrode input signal may be used in combination with many other electrode input signals to define multiple referential signal channels.
A combination referential and differential amplifier circuit in accordance with the present invention also includes a plurality of medical signal amplifiers. Each of the plurality of medical signal amplifiers may be implemented in a conventional manner as a differential amplifier circuit including two amplifier inputs. The output of each of the plurality of medical signal amplifiers is the amplified difference between the signals provided at the inputs to each of the medical signal amplifiers. The medical signal amplifiers employed in the combination referential and differential amplifier circuit are preferably selected to operate in the frequency range of the type of electrophysiologic signals to be amplified, e.g., EEG, EMG, EP signals, etc., and to provide sufficient amplification for the given signal level of the signals of interest.
A switching device is provided between the plurality of electrode inputs and the plurality of medical signal amplifiers in a combination referential and differential amplifier circuit in accordance with the present invention. The switching device is employed for selectively coupling each of the plurality of electrode inputs of the combination referential and differential amplifier circuit to the amplifier inputs of the plurality of medical signal amplifiers. The amplifier output of medical signal amplifiers with the amplifier inputs thereof coupled via the switching device to different electrode inputs, neither of which is the reference electrode input, produces a differential amplifier signal output. The amplifier output of medical signal amplifiers with the amplifier inputs thereof coupled via the switching device to different electrode inputs, one of which is the reference electrode input, produces a referential signal output. Thus, a combination referential and differential amplifier circuit in accordance with the present invention may be employed to provide a combination of user-defined differential and referential electrophysiologic signals for display and analysis by a medical signal monitoring system.
In accordance with the present invention, the switching device preferably enables a single electrode input to be coupled simultaneously to the input of any of the plurality of medical signal amplifiers, in combination with any other electrode input, including the reference electrode input. Thus, in accordance with the present invention, a single electrophysiologic electrode input signal may be employed to generate a variety of different differential and referential electrophysiologic signals for analysis and display.
In accordance with the present invention, the switching device may preferably be implemented as a solid state integrated circuit cross-point switching device, which may be controlled by an operator to provide the desired switching device functionality. The switching device may preferably be controlled by control signals provided from the system processor of an integrated medical signal monitoring system with which a combination referential and differential amplifier circuit in accordance with the present invention is employed. The system processor may preferably generate a graphical user interface, which may be used by an operator to select which electrode inputs of the combination referential and differential amplifier circuit are to be coupled to which medical signal amplifiers of the amplifier circuit. Thus, the graphical user interface may be used by an operator to define various referential and differential electrophysiologic signal channels from the available electrode inputs. The medical signal monitoring system processor preferably controls the switching device of the combination referential and differential amplifier circuit to implement automatically the desired combination of differential and referential signal channels in response to the operator selections.
Further objects, features, and advantages of the invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings.